The present invention generally relates to apparatus for reliably shearing a coupling to a generator and, more specifically, to an apparatus for delivering sufficient torque to a shear section to cause shear section operation throughout the operational range of rotation.
Generators and other rotating machines often need a shear section or a non-shear disconnect in their drive mechanism to prevent fault propagation in the event of catastrophic failure of the driving device (gearbox) or generator/machine. This shear section will shear in the event of failure decoupling the generator from the gearbox or the prime mover. Without this shearing of the drive shaft, the failed equipment can continue rotating causing significant consequential damage to other equipment in the drive-train.
Variable speed generators require the shear section to be sized for the lowest speed and highest power, which is the maximum torque condition. However, this sizing selection creates problems at higher speeds, which can be greater than twice the minimum low speed operating point. At this higher speed, the shear section may not function as intended because the driving torque is lower for the same power level. A catastrophic failure can therefore lead to substantial damage to the generator itself and other equipment in the drive-train.
One prior art solution is disclosed in U.S. Pat. No. 6,260,667 to Sugden. Sugden uses a moving mechanism in a threaded plate located inside the main rotational shaft. This plate displaces in a bearing failure resulting in a radial offset of the rotational shaft by shearing a pin and forcing the plate axially into a mating pad creating frictional forces inducing torque to potentially shear the stub drive shaft. However, this occurs in an oil environment and the mating surfaces transmitting the torque required to shear the shaft are extremely small, which calls into question whether Sugden will induce enough torque to ensure shearing of the shaft. Sugden also creates an axial load to cause braking action, which is undesirable. The design is also complex and costly.
As can be seen, there is a need for an improved device that reliably shears at both the low speed and high torque loads and the high speed and low torque loads that can be incorporated at a low cost and simple construction to deliver reliable shearing torque.